doc(usage): plain option description (#9810)

docs/usage.md

@@ -265,7 +265,7 @@ sequelize
     logging: console.log,
     logging: console.log,
 
 
     // If plain is true, then sequelize will only return the first
     // If plain is true, then sequelize will only return the first
-    // record of the result set. In case of false it will all records.
+    // record of the result set. In case of false it will return all records.
     plain: false,
     plain: false,
 
 
     // Set this to true if you don't have a model definition for your query.
     // Set this to true if you don't have a model definition for your query.